Boron trifluoride etherate → (2',3'-Dimethoxyphenyl)-1,3-dithiane

A solution of 49.5 g (298 mmol) of 2,3-dimethoxybenzaldehyde and 48.4 g (447 mmol) of propane-1,3-dithiol in 800 mL of methylene chloride was cooled to 0° C. Boron trifluoride etherate (7.5 mL, 61 mmol) was added dropwise to the cooled solution and the reaction mixture was stirred at 0° C. for 0.5 h, then at ambient temperature for 18 h. The methylene chloride solution was washed with 2×200 mL of 10% aqueous sodium hydroxide solution, 200 mL of water and 100 mL of brine, dried over anhydrous sodium sulfate and concentrated in vacuo to give 75 g (98% yield) of 2-(2',3'-dimethoxyphenyl)-1,3-dithiane, m.p. 119°-120° C.; 1H NMR (CDCl3) δ: 1.8-2.0 (m, 1H), 2.1-2.25 (m, 1H), 2.86 (t, 1H), 2.91 (t, 1H), 3.05-3.2 (m, 2H), 3.83 (s, 3H), 3.91 (s, 3H), 5.68 (s, 1H), 6.86 (dd, 1H), 7.07 (t, 1H), 7.19 (dd, 1H).